Previously, we reported that specific metalloproteinases (MMPs), including matrilysin, stromelysin-1, stromelysin-2, stromelysin-3 interstitial collagenase, and 72 kda gelatinase were upregulated in the rhesus monkey endometrium during menstruation, which was induced by P withdrawal during the luteal-follicular transition. In this study we evaluated the effects of estrogen on MMP mRNA expression. We induced artificial menstrual cycles in spayed rhesus monkeys with Silastic implants of E2 and P. We then collected the endometrium from monkeys on days 0, 3, 5, 10 and 14 after E2 and P withdrawal. Northern blot analysis was performed on total RNA from each sample for the MMPs described above, and the MMP inhibitor TIMP-1. As expected, menstruation occurred on day 3 of hormone withdrawal. At that time, mRNA levels for matrilysin, stromelysin-1, stromelysin-2, stromelysin-3, interstitial collagenase, and 72 kda gelatinase were all elevated. The expression of some of the MMPs (e.g. stromelysin-1, stromelysin-2, and interstitial collagenase) were greatly reduced by day 5, which was identical to the pattern seen previously during the LFT. However, in the absence of E2 expression of matrilysin, stromelysin-3 and 72 kda gelatinase mRNAs remained elevated through day 14. These results indicate that E2 is not required for upregulation of these enzymes during menstruation. However, E2 may limit duration of enzyme expression for matrilysin, stromelysin-3 and 72 kda gelatinase. In summary, two patterns of enzyme expression have emerged. Type I, (eg. matrilysin, stromelysin-3 and 72 kda gelatinase) enzyme expression increases during menses and then declines in the presence of E2 but remains elevated in the absence of E2. Type II, (e.g. stromelysin-1, stromelysin-2, and, interstitial collagenase) enzyme expression is rapidly induced preceding and during menstruation only, and decreases rapidly regardless of exposure to E2.